Instrument for use on moving craft



Jan. 8, 1946- H. MURTAGH ETAL 2,392,494

l INSTRUMENT FOR USE ON MOVING\CRAFT Filed June'l9, 41.945 5 Sheets-Sheet 1 INVENTORS HUGH 4l/A2720# T//f/A? ATTORN EY Jan. s, 194s.

H. MURTAGH ETAL INSTRUMENT* FOR USE ON MOVING CRAFT Filed Julie 19 1943 34 sheets-sheet 2 INVENTCRS 1906// MUPTAGH MN A. TAYLOR Jan. 8, 1946 H. MURTAGH ETAL 2,392,494

ENS.'V/E'II'I FOR USE ON MOVING 'CRAFT V Filed June 19, 1943 3 Sheets-Sheet 3 f er,

Patented Jan. 8, 19x46 INSTRUMENT FOR USE ON CRAFT Hugh Murtagh,Laleham-on-Thames, and John Alfred ".laylor, Kingsbury,`England Application June 19, 1943, Serial No. 491,548 In Great Britain May 28, 1942l 9 Claims. (Cl. 33-204-) This invention relates to instruments for use on moving craft, particularly on aircraft,. for determining the direction of the vertical by means of a frame which is free to tilt relatively to the craft about two horizontal axes and is gyroscopically stabilised to maintain a fixed angular relationship to the vertical, in spite of pitching or rolling of the craft. Such instruments are termed gyroverticals or gyra-horizons. More particularly the invention is concerned with instruments of this class in which freedom of the gyroscopically-stabilised frame relative to the aircraft is conferred by a cardan suspension.y In such instruments the stabilised frame may bestabilised by means of a single rotor having a. vertical spin axis, in which case the stabilised frame is identical with the rotor-bearing frame or rotor case of the eyroscope; alternatively, two rotors having horizontal axes at right angles to each other may be employed, eachv carried inV a bearing frame or rotor case, theseV bearing frames being pivoted about horizontal axes on the stabilised frame. In either case the stabilised frame is Stabilised by .the gyroscope rotor or rotors carried on it, the stabilisation being effective because the frame is free to tilt relatively to the aircraft by virtue of the. cardan suspension.

In known. types of gyro-horizon used on aircraft diiiiculties larise when the aircraftA tilts through large angles, approaching or exceeding 90, from its normal horizontal position,A as may happen in banked turns or in special manoeuvres such as looping the loop orbarrel-rolling. The difiicultiesare due to the fact that one of gimbal axes of the gyroscope comes into line, or nearly into line, with another axis to whichy it is normally perpendicular, and the gyroscope then loses one degree of freedom and ceases to operate inthe I normal manner. For example, in the case lof. a

gyro-horizon having a single rotor with vertical axiswhose rotor case is mounted in gimbals havingfore-and-aft and transverse gimbal,Y axes, a manoeuvrey of the craft may result in the outer gimbal axis coming intov line with the rotor axis. All three axes ofthe gyroscope then lie instantaneously in a'- plane and the gyroscope has no freedom. in this plane. Angular movement of the craft in this p lane therefore causes violent. precession of the gyroscope. Furthermore, when the outer axis and the rotor axis are in line, there is. a tendency for the cardan ring and rotor case to turn, or even in some cases to spin, about the common axis ofthe rotor and the outer gimbals; the angular position of the gimbal. ring is: thereby disturbed. which. causes subsequent. errors in the indications of the instrument, and leads in turn to the application of further disturbing torques to the gyroscope as the craft completes its manoeuvre. A still more serious defect is that, if the outer gimbal axis does come into line with the rotor axis and the girnbal system does spin round the rotor axis, the gyroscope is thereafter forced to follow the movements: of the craft. and cannot free itself from the spinning gimbals.

The invention aims at avoiding these. defects in prior types of gyra-horizon. It provides a gyrohorizonk in. which` the Vgyroscopically stabilised frameA remains stabilised and undisturbed during inclinations o1" the craft onwhich it is carried up toand exceeding 90, and in fact during all the recognised acrobatic manoeuvres that an aircraft may carry out, including complete loops, complete; rolls, and half-loops followed by half rolls.

According to the invention the improved gyrohorizon comprises a frame carrying one or more lstabilising gyroscopes, this frame being supportedv with freedom to turn relatively to the craft about two mutually perpendicular horizontal axes by means of a suspension of the cardan type which is arranged.` so that the gimbal frames are free to rotate about their vaxes of `support throughout 360, and so that the stabilisedframe retains two degrees. of rotational freedomrelative to the craft even if the craft-becomes inclined through 90 from its normal horizontal position or carries out such acrobatic manoeuvres as a complete loop, a complete roll, or a half-loop followed by va halfroll.

In one embodiment of the invention described in more detailhereinafter the gyro-horizon has a single rotor spinning about a vertical axis inf-a rotor' case,l or rotor-bearing frame, which is supported in a supporting frame by means of a car- `dan suspensionadapted to provide the rotor.-

bearing framey with. two degrees of precessional freedom Vrelative 'tothe supporting frame, each extending throughout 360",l aboutrtwo mutuall-y perpendicular horizon-tal axes, and the said supporting frame also is mounted for rotationalfreedom throughout 360 in: an outer support and is gravity-controlled.

In this gym-horizonneither of` the'gimbal axes y by which the rotor case is suspended from the gravity-controlledsupporting frame can come into line with the rotor axis during flight of the aircraft, even if. the aircraft carries out acrobatic manoeuvres; the gyroscope therefore alwaysv has three degrees of freedom-fone of rotation and two of. precession. This results from,Y the fact that the outer gimbal. axis is' always controlled of the rotor case, gimbal rings, and gravity-com' trolled frame, is then free to turn about `the Ver,-` tical axis; however, this condition can only Yexist momentarily, and, as soon asuthe axis of support departs again from the vertical, theA gravity-com;r

It is true thatv axis is parallel toth'e fore-and-aft axis of the craft. Within the frame I there is journalled a gimbal ring I by means of pivots 8, 9 supported V in ball bearings 8', 9'. The ring I0 normally lies trolled frame is once more definitely positioned` V by gravity about its axis of support, and the Vin,Y

strument operates as before without any' perma-Vv nent change in the position of the gimbalframe due to the vtemporary alignment of the two axes. Furthermore, during the whole period of the manoeuvreunder consideration, -even when the axisof the gravity-controlled frame is in line with 'the rotorjspin axis, the gyroscope hasth'ree degrees of freedomA so that torques cannot be trans'- mitted from the craft through the gimbal system tojproduce forcible precession of the gyroscope.

VVIn order that Vthe invention may be clearly understood and-readily carried into effect, it will now be described more *fullyl with reference to the accompanying drawings nwhich vFigure 1 is a'sectional planview of 'anr instrument constituting one embodiment of the present invention. f' y -Y Y Figure 2 isr an elevation, partly in section, in the vertical plane. f Y g j f 'Figure Sis a plan view from inside the rotor case of certain ports therein and control shutters therefor. Y f

Figure 4 is an elevation of the rotor casel viewed 'transversely corresponding to the plan View of .Figure3f-vy l Figures 5 and 6 correspond; closely with Figures -3 and-l-re'spectively but show the instrument -tilted-anticlockwise about the transverse axis.,` Y`-1ligure 7 isY aplan-view of the rotorcase corresponding clselywith Figures 3 and' 5 but shows the effect onfthefports andshutters ofa tilt of the Vinstrument-clockwise 'about 'the' fore-andaftaxis. Y l Y Figure 8 is related toFigure 'IH in that it is an elevation taken in the fore-and-aft directionof the rotor `case whentilted clockwise about'the fore-and-aft axis; it should be understood therefore that Figure 7 is turned 90 with respect to Figure 8. Y Y

VFigures 9 to 13 are views of the indications seen on looking at the front or face of the instrument shown in Figures 1 and- 2 under diierent condi`4 tions of flight of the craft carrying vthe instru` ment. Figure 9 represents the indications provided duringalevel flight; Figure Vl0 those provided during ardive; Figure -11 those provided Whenthe craft is banked to the left without turning; Figure 12 those provided during a climb and turn to the right with correct bank; and Figure 13 those provided during a turn to the left with an insuicient angle of bank. Y I

In Figs. 1 and-2, the .reference numeral I de-` notes the instrument case, while 2 is an observa` tion Window. The case Ihas a tubular extension v'and is normallylhorizontal, soY thatii in a horizontal plane but is free to undergo complete revolutions relativeto the supporting frame 1 about the axis BB defined by the bearings 8', 91,1'Which. axis r is perpendicular 'f to the axis AA coincides with th'e transverse axis of the craft when the craft is flying horizontally. Within the gimbal ring I0 there is journalled the roto!` case I3 by means of Ypivots II, YI2 supported in ball bearings `II', I2.. The rotor case I3 is free tc undergo complete revolutions relative to the gimbal ring VII) about the axis CC' defined by the bearings II', I2', which axis is yperpendicular to BB and is normally horizontal and is therefore normally in line with' the axis AA', i. e., when the craft is fiying horizontally. The rotor M spins in bearings Y(not shown) about anormally vertical axis DD' inthe rotorcase I3.V i Y 1 Attached to the backof the instrument case is a cylindrical cover I5 (of negauze) with a' cap IB';` these together enclose'a space I1 surround'- ingth'e extension B'of the instrument casing. The Vstern B o-f the' forkedr gimbal-supportin'g framer'l is tubular, and itsV boreV I8 is in cornmunication with' the space Il. ,The interior space Y I9 of the instrument casing I Vis substantially shut off from communication withA the space II by a partition I9' which Aextends inwards from`Y the tubularextension 3 of the instrument case. The partition I9 definitely clears the stem 5, but the clearance is smallenoughto opposea high resistance to the flow of airrthroughit. The bore I8 in the'stem-I is in communicationv with passages 20, 2I fin the forked gimbalV frame 1, and these in turn communicate, via passages ,22, 23 inthe vpivots 8, 9,'Wthpassages 24, 25 in the gimbal ringV II),V whichv passages communicatevia passages 26, Z'Iin the pivots II, I2, with passages 28,' 29 in the rotor case- I3. The passages 28, 29 open vintothe interior of th'e rotor case in directions substantially tangential to the rotor I4.

' The rotor case I3 totally encloses the rotor and is air-tight except for six ports. Two of these are the pas'sages28; 29falready described by which air entersl to spin the rotor. In addition'there are fourexitpcrtssu, 3c', 3|, 3|' (Figs. 3 to e) directed vertically 4'downwards through thebottom of the rotor case by which air can leave the rotor 'case and pass into thespace I9 in the instrument casing I.` 'This space I9 is maintained at a pres'- Vsure below atmospheric'pressure by 'means 'of a suction pump, not shown, the instrument casing I being otherwiseair'tight. v

When thesuction pump Y1s operating, airis sucked in through` the Vcylindrical ne gauzel cover f 3|' may be uncovered'into the space I9 inside'theV casingI from whichit* is finally extracted by they suction pump; The airfthus entering theinterior of the rotor case YI3`from the passages 28,' 29 does so in the'forrn ofxhighvelocity jets; theseraref so directed as to impinge against buckets 32 Vcut on the periphery ofV the rotor I4, soY that the rotor is spun at a high angular velocity. The spent'air circulates in the interior of the casing yI31'and nallyissues from the jets 30,30', 3|, 3|' asrjets of app'reciabl'ezvelcity. i f i 'The ports3; 3Il'ar'e spacedat equal' distances llaterally from the centre of the gyroscope (dened as "the intersection of theaxes BB'f, `CC") and are so designed that the air jets issuing from them whenthe ports are uncovered exert equal .is balanced by anv equal oppositely acting` jet.

The laterally spacedv jets 30 30' are variably controlled by means responsive to relative inclinationabout the axis BB' (i. e., relative pitch) of the rotor oase I3 on the one'hand and the di, rection of the resultant of the gravity and acceleration iields on the other hand. As shown, -this result is obtained by the, provision of shut- -ters,33, 33',l whichform part of a, pendulous stirrup-shaped shutter' frame 34 and which variably intercept the jets 30, 30' in accordance with the tilt. of rotor case I3 relative to the shutter frame 34. The frame 34 is pivot-,ally mountedabout an axis parallel to BB' by pivots 35, "35, supported in bearings in the upper part of the rotor case I3. In the normal relative position of the rotor cas-v ing I3 and the pendulous shutter frame 34 shown in. Figs. 3 and 4.-vvhich is that taken up, for example, when the axis of the rotor I4 is vertical and the pendulous shutter frame 34 is hanging freely under gravity and when no acceleration forces. are operatingthe shutters 33, .33.' intercept, the jets 30, '30' to equal extents-viz. -they intercept substantially one-half of each jet. If this relative position is disturbed,l e. g., by precessional tilting of the gyroscope about the transverse axis BB (pitch) as shown in Figs. 5 and 6, asA a result of frictional. torques, one of the jets 3l), 30' is uncovered byqlits shutter 33 or 33 toa greater extent than normal and the other to a less extent, with the result that an unbalanced air jet reaction is applied to the rotor case. VThis unbalanced air' jet reaction applies a torqueto the rotor case I3 about Vthe axis CC' and thus causes the' rotor case to precess aboutthe gimbalV axis BBI'baclrf towardsfthe normal position of alignment with the shutter frame 34. Preferably the rotory case I3l is in'substantially neutral equilibrium about the axis CC', and the combination of rotor case I3 and inner .gimbal frame I0 is in substantially neutral equilibrium about the axis BB' so that no direct gravitational torques are exerted if tilting of the gyroscope should occur. Consequently, if the gyroscope should tilt about the transverse axis BB', the torques exerted by the air jetsv30, 30' are the only ones that operate, and these produce erection of the gyroscope back to the vertical position in the planey of tilt without the occurrence of any conical oscillation.

Similarly jets 3l, 3l are controlled by shutters 33, 39' forming part of the pendulous lstirrupshaped frame 40 in accordance with relative tilt ofthe rotor case and the shutter frame 40.

As can be seen in Figure 8 the upright arms of the stirrup-shaped frame 40 are curved round the bosses of the pivots I I, I2 so that the frame can swing freely throughy a small angle about the pivotsA 36, 36 without fouling these* pivotA bosses.

` In- Figs. 7 and 8 the conditions holding good during a. .'precessional` Vtilt of the-rotor case I3 83201131,- the fore-and-aft axis CC? are` illustrated.

Asshownthe air jet. nozzle 3i isy uncovered bythe .shutter 39Lwhilenozzle 3l' lis covered `by the Vshutterv 39'.V .An vunbalanced, reaction torque about the axis BB is therefore exerted ,by the air jetv from nozzle 3|; this causes the rotor and rotor case to precess about` the axis CC' back 4into alignment Withthe frame 40.

The extent of the possible angular movement of the frames 34, 4I)` about the pivot axis 35--35' and 36-36' relative to the. rotor case I 3 is limited by stops 3:?, 31. and 38, 38," respectively, so that Figs. 5 and 6 represen-t the conditions holding good during relative inclinations of the rotor case I3 and frame 34, and Figs.. '7 and 8 those during relative tilts. of the rotor case I3 and Vframe 4t), not only through the angle shown, but

through any greater angle,

The use, of pendulous shutters for controlling air jets issuing from the rotor case of a substantially neutral gyro-horizon so as to cause erect..v

ing torques to be applied, in a manner similar to that described herein in connection with the ports 30, 30', 3l, 3l and the shutters 33, 33', 39, 3S', is 'described and claimed in Patentv No. 1,982,636, dated Decemberfl, 1934, for Air driven gyro verticale. However, in the present embodimentr of the invention, in order to reducer the overall dimensions Vof the rotor case I3 and thus to permit the rotor case to undergo complete revolutions about each of the horizontal axes of support BB' and CC', without any increase in the diameter ofthe instrument case I, the shutters 33, 33', 39, 39' are mounted in the novel manner hereinbefore described, i. e., the shut.- ters 33, 33 of a pair are linked together by a frame 34 external to vthe gyroscope and .this frame is mounted on a pair of pivots instead. of on an axle passing through the rotor case. In this Way the pendulous shutter frames can be pivoted on any axis Whatever in the rotor case, and there is no need to provide an extension of the. rotor case below the lower bearing of the rotor to carry a pivot shaft for the pendulous shutters.

The gyroscope of the present invention is of the type that is generally known as a gyroscope with three degrees of freedom, since the rotor is free to turn, i. e., rotate, about the axis DD and this axis is free to turn, i. e., precess, in two perpendicular planes, each containing the rotor axis. Precessional freedom in the plane DD', BB is conferred by the: freedom of the rotor case I3 to turn abouty the inner gimbal axis CC' in the gimbal ring I0. Precessional freedom in the plane DD', CC is conferred by the freedom of the girnbal ring4 I=0 to turn about the outer gimbal axis BB in the forked gimbal frame 1. Thus the rotor has one degree of rotational freedom and two degrees of to the frame 1..

In previous three-degrees-of-freedom gyroscopes used as inclination indicating instruments for vehicles such as aircraft the frame relative to which the rotor had three degrees of freedom was the vehicle itself or was a frame rigidly or reprecessional freedom relative' v ing.

, gimbal axis CC).

4 velocity. in this p1ane,the` gyroscope is caused to precess violently inthe plane normal'to the. axis y CC'. In practice the' gyroscope is very liable to `be disturbed if the axis BB' approaches to'within or.l0 of the direction of'therotor aXis DD'.

vThereafter the instrument would give indications friction or'air currents, sincethere is nothing to restrain such rotational displacement nor to define a position forA theassembly about this comf mon axis. If the assembly should turn about the common axis, further manoeuvres of the craft taking'the axis BB' out.; of line with DD' can exert furtherv disturbing jtorques' on the gyroscope.V It may even happenin some cases that,

vif the axis BB' comes intoline with the axis DD',

the assembly of rotor case vI3 and gimbal ring I0 may start to'spin continuously about the common In that case it may become impossible' for the axis DD'. to escape from alignmentwith. the axis BB' because an incipientescape vfrom alignment in any particular direction is suppressed as thegimbal ring I3 turns about BB' towards the direction .in which DD' is escap- When the gimbal ringapproaches this positionV a kind of toggle .action takes place by which the axis DD' is forced back into alignment with the axis `BBZ'the force exerting the toggle tov effect this being derived from the angular momentum of the gi'mbal ring. As a result of -this action the rotor is forcibly precessed to follow all movements of the'axis BB', i. e., all movements of theA craft.

In the present invention these defects of prior instruments are overcome by providing the frame with freedom to turn relatively to the instrument casing l and by governing the frame 1 by gravity. `It is for this purpose that the frame 1 isrrotatably mounted in the casing I about the axis AA' (whichis normally in line with the inner Gravitational control of the frameV 1 about the axis AA' may readily be obitained vby making the frame simply pendulous about this axis, e. g., by arranging that the axis BB' lies below the horizontal plane through AA. Howeverfwe prefer to effect gravitational control .in another manner, which will now be explained.

' In the frame 1 there are secured two vertical cylindrical containers 4 I, 42, symmetrically placed ,with respect to the axis AA'. These are partly filled with liquid, e. g., `with mercury. Wheny the containers are empty the forked frame 1 together with the parts of the gyroscope that it serves to support are in neutral equilibrium aboutthe axis AA', so that the addition of the mercury. makes the frame 1 as a wholel pendulous about the axis AA'. f

It can readily be about Vthe axis AA' to .an angle of nearly 90 or rolls completely over about this axis, the axis BB' will not come into line with theV axis DD. VIf there Wereno side-slip, the axis BBwould stay y horizontal and therefore at right angles to DD';

actually side-slip does occur down the inclined plane of the wings and the acceleration down this plane tends to leave behind the pendulous liquid in the containers 4I, 42,y so that the pendulous frame 1 does turn about the axis AA'-, however, itdoes not turn through an angle even approach- 'ihgQU-'f S0 that the. axis BB'. always.l continues@ .make a large angle'with DD and the gyroscope seen that, if the aircraft banks Y has still to continues to retain three degrees of freedom.

i It might be expected that one degree of freedom would be lost if the aircraft were to pitch upwards through thereby bringing the axis AA into line with` the rotor axis DD. In spite of this the gyroscope still retains three degrees of freedom about DD', CC' and BB'. Nevertheless, it is of 'interest toinvestigate the second difficulty exL Vperienced in prior instrumentswhen` normally vdifferent axes come into alignment, namely rotation of the gimbal frame. vIt is true that, if the axes AA', DD', come into line, the whole assemblyy of rotor case I3, gimbal ring I0, and outer frame '1, becomes free to rotate about the common axis AA', DD. However, Veven if this assembly-does become angularly displaced about the common axis, the gyroscope retains three degrees atreach position, so that torques cannot be transmitted through 'the gimbal system to disturb the gyroscope. Y

The possibility that the gimbal system may start spinning round the common axis AA'-, DD' V be considered. This is veryunlikely inthe instrument of the invention, as one of the main causes of such spinning is abnormal frictional forces between the rotor and the rotor case resulting from abnormal bearingstresses due to forced preces'sion of the gyroscope,` and these cannot exist in the new instrument owing to the absence of forced precession due to the `continu ous retention Yof three degrees of freedom. Also rotation of the rotor case and gimbal assembly round the common axis, even if it should occur, cannot forcibly suppress incipient escape of the axis DD' from alignment with the axis AA because there is no angular` position round the common axisin which one of the three degrees of freedom is lost, so that the toggleaction that caused forced precession in prior instruments does not take place. l Y

Finally, as the aircraft completes its manoeuvre and the axis AA' ceases to be vertical, the gravity control of the frame 1etakes effect again and this frame is brought at each instant into a position depending only on the attitude and motion of the craft at that instant. It follows that, even if the axis AA' does come into line with the axis DD", not only vwill the gyroscope rotor not be dis'- tur'bed but also the angular position off the gimbal frames is very unlikely to be appreciably disturbed. It is possible that the position of the gimbal frames will be disturbed instantaneously when the craft is climbing or diving vertically and the axis AA' is actually inline with the axis DD', but, even then, this disturbance is annulled by the action of the gravity control on the frame 1 immediately the aircraft changes its attitude Yand takes the axis AA cut of alignment-with stant, inY exactly the same manner as if thev craft had never passed through a vertical climb or dive attitude. j

Consideration of theoperation of the instrument during a manoeuvre by the craft consisting of a half-loop followed by an interval of straight flight in an upside-,down position and a half roll brings out additional features of the invention;

, During the half-loop strong centrifugalforces 'cury in th'e containers 4I, 42.

are actingV relativelyto the aircraftion' the' mer.-

1 These forces rvact radially outwards from the centre of lthe curved path of the `rloop and 'thus act along towardstlie floor gof the'cabin or cockpit even when the air-n' craft is climbing vertically and even. towards the'V end of the half-loop when thelaircraft is almost wholly inverted. The, centrifugal acceleration. is greater than the acceleration-of gravity, so the gimbal frame 1 is acted on by a resultant force towards the floor of they c-abin and thus doesnot turn `relatively to the instrument casing Towards the end of the half-loop, justfore the aircrafts path straightens out, the aircraft is flying upside-down, so that the ends 4|, 42'? of thecontainers 4|, 42 are uppermost, the mercury being held in these ends by centrifugal force. When the aircrafts path straightens out, the centrifugal force vanishes and gravity acts alone; the mercury in the containers 4|, 42 at once falls to ends 4|', 42', which are at `this time the lower ends, and no change occurs inthe position of the gimbal rings relative to the aircraft. This behaviour of the instrument may be contrasted with what would occur if the gravity control of the frame 1 were effected, not by employing liquid in the containers 4 I, 42, but by the rigid attachment` to the frame of ,pendulous masses. Such an instrument would behave in most circumstances in the same manner asthe instrument so far described, but, at the top of thehalf-loop manoeuvre when the aircraft straightens out andV centrifugal force ceases lto operate, the frame would be left in a top-heavy condition. In this position the instrument would be unstable, and,

perhaps after an instant of rest in the position of unstable equilibrium, the pendulous frame l would turn through 180 round the axis AA' to lower its centre of gravity, taking with it the gimbal ring I which would turn relatively to the rotor case round the axis CC. An instrument of this character is within the scope of the invention, lbut we prefer to avoid the sudden inversion of the frames 1 and the ring l0 that occurs in it at the end of a half-loop by adopting the principle illustrated in the drawings of `providing gravity control of the frame 1 by means of displaceable masses, i. e., the liquid in the containers 4|, 42, so arranged that, if the frame 1 is inverted the masses move relatively to the frame into new lower positions available to them, whereby the frame is then gravitationally stable in its'inverted position.

If'the aircraft, after completing a half-loop and ying Vupside-down;l carries out a half-roll, the wholeassembly of rotor case i3, gimb-al ringy is illustrated inV the drawings and this will now be described. On the two ends of the gimbal ring I0 there are mounted part-spherical screens 43, 44, uniformly coloured in some neutral shade to serve as a background for the indications. Through `these screens there protrude rods, 45, 46,y extending from the rotor-case pivotsil, I2. On the outer ends of these rods there aremounted discs 41, 48 and also Vvertical pointers 49, 49'; 50, 50', the latter-being curved in the vertical plane containing them so as to lie close to the screens 43, y44.` The-indications ofthe attitude of the craft are provided by the relation between whichever of the discs 41, 481 with its associated i pointer 49, 45 or 50, 50V is visible in the window,

on the one hand, andy certain cooperating reference members or markings'fixed'relative to the instrumentcase, on the other hand. There are two of these fixed reference members or markings, both carried on an A,annular ring 5| surrounding the window `opening on the inside of the window glass 2. 'I'he first is a strip 52 (Fig. 9), extending diametrically across the' annularr ring 5|, and having a form suggestive of an aeroplane in end-on flight away from the observer.

The central portion of this 'figure consists of` a ring 53, suggestive of the fuselage vof the aeroplane, and just large enough to surround the disc 41 when the latter is central in the window: The second reference `marking consistso a set of widely spaced bank vangle graduations 54 provided on the upper part of the ring 5 I; these are readable against the gyroscopically stabilised vertical pointer 49; the wordsY Right Vand ;Left are associated with them to indicate right bank or left bank respectively. If Fig. 10, which shows the indicationsprovidedduring a dive, is contrasted with Fig. 9,'which shows the indica-v tions during level flight, it can be ,seen vthat the disc 41 moves down during a dive. 'Ihe pilot may I0, and pendulous frame 1 is unaffected and the f aircraft Vmerely rolls round the frame 'l about thev axis AA. AI'he relations between the craft andthe gyroscope during the whole manoeuvre may be described by the statement that the craft and the frame 1 first turn through 180 round the gyroscope about the axisy BB and then the craft turns round the gyroscope and frame 1 about the axis AA'. It is evident therefore that nally there is visible in thev window 2 that part of the 'gimbal ring i0 which was initially remote from the Window. The invention aims at ensuring that after this manuvre the gyroscope still provides information in the same manner as before concerning further changes in the attitude of the craft, which is now flying horizontally. The gyroscope is therefore provided with means for indicating the-attitude of the craft whether the gimbal rring I0 is in the positionA shewn' in the ldrawings or is turned'through 180 about the axis BB'.

1t is'possible to provide indications satisfying,r these requirements in several ways; one of theseV therefore consider the disc'41 to' represent the nose of the aircraft;` it is for this reasonv that theindex 41 is chosen to be of disc form so to be suggestive of a propeller boss orspirin'er. If Fig. 11, which represents the conditions 'durf ing a bank to the left, is compared withthe level flight conditions of Fie. il,y it can'be" seen that'the'" relation of the'aeroplane gure 52 tothe vertical" line 49 immediately conveys' to the observer the ideas right wing up, left wing down, i. el, bank to the left.

Fig. 12 shows the indications occurring during the combination of a climb and a right bank. Although in this figure the Anose 41 is not in the plane of symmetry of the wings of the 'aero-` plane figure 52, so that the indications provided do not pictorially represent the actual conditions in every detail, it remains true that Fig. 12 does convey pictorially the ideas nose up, left wing up, right wing down, i.-e., climb, and bank to right. Y e, 1 The condition shown in Fig. 11, which. has. been described as a bank to the left, results :fro-1n` a rotation of the craft about its fore-and-aft axis.k

If the craft is diving very steeply, a rotation about. i

the fore-and-aft axis becomes a spin rather than a bank. It is desirable that any tendency to spin Y should be indicated in a clear manner. However, "n

bank indicator 49,' 49',

159, 56', are therefore nolonger visible in the win-v dow. Accordingly additional pointers are provided in the form of narrow bars 55, 56, (Fig, 2)

lying in the plane of the pointers 49, 49' and 50, Y

50'; these additional pointersA are carried by the vrotor case I3 and are adapted to pass inside the `gimbal ring I6 if the latter rotates around the rotor case I3 about the axis CC'.

an indication of the centralvertical plane of the `gyroscope which is continuous all round the axis BB'. The instrument therefore achieves therevsult that a turn about the fore-and-aft axis of the craft is indicated in the same general manner,

`no Ymatter how steeply this axis isginclined.

In the gyro-horizon of the invention, advantage may be taken of the fact that the forked frame 1 is pendulous to Vcause the instru-ment to furnish an indication Yoi? the false vertical for `comparison with the true vertical indication provided by the gyroscope. The instrument illustrated in the drawings includes this additional feature. As shown, a light metal annular frame 51 is fixed on the'endfof thel forked frame 1 near to the window 2. From this frame two arms 58,

,V59 project forwardsl towards the window 2 over 1 and underthe part-spherical screen 43. These arms terminate in pointers 6l), 6! which lie close `to the verge ring 5I and between this` ring and the vertical pointers 49, 49'.Y 62 is provided on the lower part of the verge ring 5I, on which scale the angular Yposition of the A scale of degrees pointer 6| may be read.

'I'he position of the-pointer 6i on the scale 62 may be used as a correct-bank or side-slip indi- 1 cator, since the pointer 6I, by virtue of its attach- 1Vment to the pendulous frame 1, (by way of the arm 59 and annular ring 51) hangs in the false vertical defined by the resultant of gravity and ,the lateralacceleration forces, such as the ceny trifugalforces operating during a turn. When the pointer 6I remains on the zero'mark of scale Thus the Y pointers 49, 49', 5U, 50', and 55 Vand 56 provideV Yassitance.` Y

be used 'as the" angle to Vwhich during a turn.k l

What we claim is: Y

y 1.. Anaircraftgyro horizon comprisingV a'rotorV frame, a gimbal ring pivotally mounting the- Vframe on said ring for movement about a normally horizontal axis, a second gimbal ring pivotally Ymounting the first gimbal ring for movement about a normally yhorizontal axis perpendicular to said first axis, said; frame being thereby uni-A versally supported in neutralY equilibrium, 'an'` outer-support in which said secondV gimbalring is mounted for movement about an axis parallel fto 4or in line with said first' axis, said second ring being pendulously mounted, and attitude in-vv dications on both the front and back and top and bottom of said frame, whereby the instru-A may be read in any' ment remains operative and attitude of the craft;

2. In an aircraft gyro horizon, a casing,` a

pendulous first gimbal pivoted inY said casing on an axis normally corresponding to the roll axis of the'craft, a second gimbal'pivoted on said? first gimbal on an axis normally corresponding to the pitch axis of the craft, a rotor frame comprising a reference fixed to said pendulous vrs't gimbal cooperating withthe indexfof said y roll indicating means.

3. A gyro horizon for aircraft, comprising` a support, a first gimbal pivoted therein ona roll axis, a second gimbal pivoted on said rst gimbal l Yon a pitch axis, a Vrotorjframe pivoted on` said 62 during a turn as shown in Figure 12, the air- Y v, craft is correctly banked; if, however, the pointer 6| is to theright of the zero mark'of scale`62, as

i shown inxFig. 13, the aircraft is side-slipping to l the right, and it is therefore necessary, in order to correct this condition,thatthe' aircraft should zero mark of scale 62 into line withthepointer be banked more steeply to the leftto bring the o 6| Incidentally, it may be noted that thedirectionin which the aircraft has-to be banked-is readily ascertainable from the fact that it is the Y direction in which the aeroplane gure 52 must be `banked to become symmetrically disposedfwith I respectjto the'pendulous'pointer 6l,v If desired an indication of banking may be obtained from i the point Vdiametrically opposite the 'pointerV 6I with reference to the referencemark54. Y

It might seem that the information concerningV side-slip or correct banking that is provided b3r` the pointer 6l could Ybe provided by any pendulous indicator even if this were not associated with the n i gyro-horizon. However, Vspecial advantages are obtained by the featurev of ,the invention accord- 1 ing towhich the pendulous indicator 6| turnsv second gimba1 on an axis normally coincident with the roll axis of the first gimbal, said'first gimbal being pendulous, aY stationary vroll index on said support, an indicator on said rst 'gimbal cooperating with said index-to -show'side slip ofV the craft, and a second indicator onV a trunnion'of said rotor frame cooperatingr with said index to show the attitude of the craft about its roll axis.

4. In an aircraft gyro horizon, a casing, apendulous rst gimbal mounted in said casingr 'for movement about 'a horizontalaxis, a second gimbal mounted on said 'first gimbal for movement Y about a normallyY horizontal axis perpendicular to the axis of the iirst gimbal, a rotor frame -pivotally mounted on said second gimbal on an axis normally in alignment-with the axis of said rst f Y gimbal, and pitch indicating means comprising an index xed to said casing and a pair of references therefor, one of rwhich is observable at Y a time with the index, said references Ybeing movable with the rotor frame. about the axis thereof normally in alignmentwith that of the first gimbal and 4being situated Yon oppositersides of said frame. Y 5. A-universal gyro horizon having, inaddition to its rotor bearing frame and gimbal mountabout the same fore-and-aft axisas a gyroscopic i it can readily be'seen from the stabilised pointer This advantage is that,

` 49, 49V whether the pendulous'pointer6l is steady or swinging, and, ifY the pendulous pointer 6l 'is swinging, Vthe stabilised pointer 49,' 49'V provides ,Y a referencebackground for it`s`o that the mean fposition'of its swings can be appreciated and can ing, an auxiliary gimbal ring having a .major axis normally in line with one of the axes of the said frame, gravitationally displaceable means for rendering said auxiliary gimbal'pendulous ineither of two horizontal positions, and horizon indicating means mounted on both the front and backA 'Y and top and bottom of said frame so that one of said indicators is always readable Without resetting during stunt ying and said auxiliary gimbal to bank ycraft remains in either of two horizontal positions of equilibrium.

6. In a gyro horizon for aircraft, a casing having a rotor frame mounted for freedom about a major athwartship axis and a minor fore and aft axis, fixed markings on the window face of said casing comprising a normally horizontal representation of wings and a central ring, a disc secured to each minor trunnion axis of said frame, one of said discs normally occupying the central position in said ring and representing the nose of the craft, and a roll or bank reference extending both above and below each disc, whereby said indicator is always operative regardless of which end the frame is\viewed from.

7. In a gyro horizon for aircraft, a casing having a rotor frame mounted for freedom about a major athwartship axis and a minor fore and aft axis, xed markings on the window face of said casing comprising a normally horizontal representation of wings and a central ring, a symmetrical member secured to a minor trunnion axis of the `frame normally occupying the central position in said ring and representing the nose of the craft, whereby pitch is indicated by up or down displacement of said member from its normal central position in said ring, a pendulously mounted side slip indicator, a roll scale on said casing on which said indicator is readable, and a roll reference extending from said member and also readable on said scale, whereby the angle of bank of the craft is shown with respect to both the real and virtual vertical.

8. An aircraft gyro horizon comprising a rotor frame, a gimbal ring pivotally mounting the frame on said ring for movement about a normally horizontal axis, a second gmbal ring-Divotally mounting the rst gimfbal ring for movement about a normally horizontal axis perpendicular to said first axis, said frame being thereby universally supported in neutral equilibrium, an outer support in which said second gimbal ring is mounted for movement about an axis parallel to or in line with said first axis, and a liquid container partially filled with liquid mounted on said second gimbal ring and extending both above and below its axis within the support, whereby said gimbal has two positions of equilibrium degrees from each other.

9. In a gyro horizon for aircraft, a casing having a rtor frame therein mounted for movement about a major axis corresponding to the athwartship axis of the craft and a minor axisv corresponding to the fore and aft axis of the craft, combined pitch and roll indicating means comprising an index fixed to said casing in the form of a normally horizontal representation of wings and a central ring, a reference disc for said pitch index secured to the minor axis of said frame, whereby it is stabilized in roll and pitch, said disc normally occupying a centralized position within said ring, and a vertically extending pointer secured to and extending above and below said disc whereby pitching of the craft is indicated by vertical displacement of said disc with respect to said ring and rolling is indicated by relative inclination between said index and said pointer.

HUGH MURTAGH. JOHN ALFRED TAYLOR. 

